The present invention relates to hand power tools.
German reference DE 197 26 383 discloses a hand power tool which is an electrically driven hammer drill. The hammer drill has a work spindle which is rotatably driven and supported in a housing and drives a tool receptable for a tool. Furthermore, the hammer drill has a mechanical striking mechanism which has a striker axially displaceable in the work spindle formed as a hollow shaft and accelerated in an axial direction. During the operation it acts directly or indirectly on the shaft of the tool. A drive unit acts on the striker. It derives an axial acceleration of the strike from the rotational movement of the work spindle. The drive unit includes a sensing unit which rotates synchronously with the work spindle and is axially displaceable. It is guided with an axial gap between two ring shaped curved tracks non rotatably arranged relative to the working spindle and provided with raised portions and depressed portions arranged near one another in an axial direction of the work spindle. The sensing unit is formed as a ring-shaped component which is supported axially displaceably on the striker in an axial direction against a pressure spring. It has a radially outwardly extending sensing unit which engages through a slot in the work spindle between the curved tracks and is bringable in operative connection with the curved tracks via the sensing unit.
The curved track which faces the tool is axially displaceably supported for turning on and turning off of the striking mechanism together with the work spindle. If the tool is pressed against a surface to be treated, the work spindle and the curved track facing the tool displaces in direction of the curved track facing away from the tool axially against an idle spring which is formed as a pressure spring. Therefore the sensing member during a rotational movement comes to abutment with the both curved tracks. The impact mechanism is turned on.
If the tool is lifted from the surface to be treated, the curved track which faces the tool and the working spindle is moved back by the idle running spring to its initial position. The distance between both curved tracks is therefore increased so that the sensing member can rotate freely between the both curved tracks without coming to abutment with them. The striking mechanism is turned off.
It is therefore an object of the present invention to provide a hand power tool which avoids the disadvantages of the prior art.
More particularly it is an object of the invention to provide such a hand power tool, in particular an impact drilling power tool which has a drive means which is drivably supported in a housing, a mechanical striking mechanism for a striking drive of a tool in a tool receptacle and having a striker which is drivable in its striking movement via a drive movement, the at least one curved track with raised and depressed portions located near one another in an axial direction of the tool and with a sensing unit which is inoperative connection with said striker and has at least one sensing unit which is bringable in an operative connection with the raised and depressed portions of the curved track.
In particular in impact drilling power tools with a quick clamping chuck or a toothed rim drilling chuck and a full shaft, in a simple and cost favorable manner an advantageous striking mechanism with a striker can be provided. Recommended standard components can be substantially retained and an expensive new constructions can be avoided. Furthermore, hollow shafts for guidance of the striker can be avoided and thereby required costs can be saved. The inventive solution can be used in a structurally simple manner for other hand power tools, such as for example for scrapers, etc.
When the drive means is supported axially displaceably, and a projection of a drive means in direction of tool receptacle forms an abutment for the striker, additional components, structural space, mounting expenses and costs can be avoided, and in a structurally simple and efficient manner an impulse released by the striker can be transmitted to the drive means to the tool.
In accordance with a further embodiment of the present invention it is proposed to form a curved track on a cup-shaped sleeve and to arrange the projection inside the sleeve. Therefore an advantageous noise screening can be provided.
When the drive means is formed as a shaft, and at least a part of the sensing unit is connected non rotatably with the drive means and driven directly from the drive means, additional components for rotary transmission are avoided and structural space, weight and mounting expenses are saved. In particular when the drive means is formed as a shaft with a small diameter, it can be of advantage that at least a part of the sensing unit is connected with a drive part which is formed separately from the drive means. An additional loading and/or weakening, for example by grooves formed in the drive means, can be avoided. Instead, a rotatably driven sensing unit can be basically rotatably drivable from the curve tracks.
In accordance with a further embodiment of the invention it is proposed that the sensing unit includes two and preferably three or more sensing members which are bringable in operative connection with the curved track or with the curved tracks. Thereby a tilting moment on the sensing unit and the striker is avoided, and a centering of the sensing unit on the curved tracks can be provided. The operational efficiency can be increased and the wear reduced.
In order to guarantee a reliable coupling and uncoupling of the striking mechanism and a reliable idle running adjustment, at least one sensing member of the sensing unit in an idle running position is limited in its movement in an axial direction of at least one, preferably two curved tracks toward both curved tracks by a corresponding abutment. When the drive means is supported axially displaceably and an abutment is formed by a means which is fixedly arranged on the drive means, such as for example a safety ring or a projection formed on the drive means, etc., an uncoupling movement of the drive means is preferably used so that an abutment can be positioned correspondingly for limiting the movement of the sensing member of the sensing unit.
Furthermore, additional components, structural space weight, and mounting expenses can be saved when the spring which is in operative connection with the striker forms at least a sensing member and/or at least a drive element of the sensing unit.
When at least one curved tracks is supported displaceably against a spring which is tensioned via the sensing unit, an especially structurally simple and cost-favorable striker can be provided.
Instead of two curved tracks, between which the sensing unit is arranged, the driver unit can be also provided with only one curved track, and exclusively with such a curved track whose raised portions and depressed portions are arranged axially in direction of the tool. The device mut be formed so that the sensing unit is moved back by a spring and/or by a strike of the striker against an abutment surface in direction of the curved track. In this case, when compared with a driver unit with two curved tracks, additional components, structural space and weight can be saved.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.